Synchronized gearbox

ABSTRACT

A motor vehicle gearbox which includes at least two parallel primary and secondary shafts, respectively connected in rotation to an engine, and through a main transmission, to a wheel. The primary shaft bears a first idler gear to a second stationary pinion borne by the secondary shaft. The first idler is capable of being jaw clutched on the primary shaft for transmitting engine power to the wheel. A self-disengaging control selectively accelerates or brakes the primary shaft which bears the idler so as to synchronize them before linking them in rotation. A self-disengaging accelerator accelerates the primary shaft if its speed is less than that of the idler, and a self-disengaging brake brakes the primary shaft if its speed is greater than that of the idler.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a motor vehicle gearbox.

The invention relates more particularly to a motor vehicle gearbox ofthe type which is provided with at least two parallel shafts, theprimary and secondary, respectively linked in rotation to a vehicleengine and, via a transmission, to at least one vehicle wheel, and ofthe type in which one of the shafts supports at least one first idlerpinion engaging with a second fixed pinion supported by the other shaft,the first pinion being capable of being linked in rotation to the shaftwhich supports it to transmit motive power from the engine to thevehicle wheel.

DISCUSSION OF THE BACKGROUND

There are known numerous gearboxes which permit the establishment ofvarious gear reduction ratios by interlocking of idler pinions on theirshafts.

In the case, for example, of a gearbox with two parallel shafts, when auser initiates the change from a first gear reduction ratio to a secondgear reduction ratio by means of a gear shift lever, the first idlerpinion corresponding to the first ratio is “released” from the firstshaft supporting it before the second idler pinion corresponding to thesecond ratio is in turn interlocked on the first shaft. Since theoperation is extremely fast, the first shaft continues to turn at aspeed close to that which it had when the first idler pinion wasinterlocked thereon. The second idler pinion, which for its part isdriven by a second fixed pinion of the other shaft with which it isengaged, turns at a speed substantially different from that of the firstshaft by virtue of a different gear reduction ratio.

To ensure that it can be interlocked on the first shaft, the secondidler pinion must be brought beforehand to a speed of rotationsubstantially equal to that of the first shaft.

This is the function conventionally assigned to devices known assynchronizers.

Each idler pinion is coupled to an axially declutchable device,generally operated by an axially movable band driven by the displacementof an operating fork parallel to the shaft supporting the idler pinion.

Once clutched, the device permits the idler pinion to be frictionally inrotation to its shaft in such a way that it progressively leads to anadequate speed of rotation without transmitting a large torque at thesame time.

In a second step (the pinion and shaft turning at the same speed), thedevice then permits the idler pinion to be linked to the shaft by means,for example, of a toothed coupling, thus establishing a gear reductionratio of the gearbox.

Such a device is advantageous in that interlocking of the idler pinionson their shafts can be facilitated thereby. In fact, since the majorityof interlocking devices are provided with toothed couplings, it isimportant that the idler pinions be synchronized beforehand with theirshaft(s) before being interlocked, in order to limit tooth wear and toguarantee noiseless operation of the interlocking device.

On the other hand, the devices provided with synchronizers have thedisadvantage of using a synchronizer based on idler pinions, thusconsiderably increasing the axial space requirement and weight of thegearbox.

In addition, in the case of a so-called robotized gearbox, or in otherwords a gearbox in which the different members are shifted bypilot-controlled actuators, these actuators being operated by anelectronic control unit on which the vehicle operator acts, the use ofsynchronizers is particularly difficult. In fact, compared with aconventional operating system with selection fingers and forks,operation of the synchronizers by actuators is particularlyinappropriate, since the actuators occupy considerable space.

SUMMARY OF THE INVENTION

To remedy these disadvantages, the method according to the invention nolonger comprises bringing the pinion to be interlocked to a speed closeto that of the shaft on which it must be interlocked, but insteadcomprises bringing the shaft on which it must be interlocked to a speedclose to that of the pinion to be interlocked.

With this objective the invention proposes a gearbox of the typedescribed hereinabove, characterized in that it is provided withcontrolled declutchable means permitting the primary shaft to beaccelerated or braked selectively in order to synchronize the speed ofthe idler pinion with that of the shaft supporting it before linking itin rotation to the said shaft, and being capable of accelerating theprimary shaft as long as its speed is lower than that of the idlerpinion and of braking the primary shaft as long as its speed is higherthan that of the idler pinion.

According to other characteristics of the invention:

the declutchable means for accelerating the primary shaft are providedwith means for temporarily linking the primary shaft in slippingrotation to the secondary shaft;

the means for linking the primary shaft in rotation to the secondaryshaft are provided with a first toothed gear coaxial with the primaryshaft, which gear engages with a second toothed gear supported by thesecondary shaft and linked in rotation thereto, the second gear beingcapable of being temporarily linked in rotation to the primary shaft viaa slipping device for coupling of acceleration;

the controlled declutchable means for braking the primary shaft areprovided with means for temporarily linking the primary shaft inslipping rotation with the gearbox case;

the means for linking the primary shaft in rotation to the gearbox caseare provided with a fixed frustoconical bearing surface of the gearboxcase, coaxial with the primary shaft, to which the primary shaft can belinked temporarily via a slipping device for coupling of braking;

the slipping devices for coupling of acceleration and of braking areprovided with a common contact wheel, which is linked in rotation to theprimary shaft by splines, which is provided with two oppositely disposedannular frustoconical bearing surfaces, and which is capable of beingdriven slidingly along the primary shaft

toward a first active extreme axial position in which a first annularfrustoconical bearing surface cooperates by friction with acomplementary annular frustoconical bearing surface of the said firsttoothed gear, to accelerate the primary shaft,

or toward a second, opposite active extreme axial position in which asecond annular frustoconical bearing surface cooperates by friction withthe fixed, annular and complementary frustoconical bearing surface ofthe gearbox case, to brake the primary shaft,

by passing through an indexed intermediate axial rest position;

the annular bearing surfaces are frustoconical;

the annular frustoconical bearing surfaces are plane, and the contactwheel is a clutch disk covered with a friction lining material;

the slipping devices for coupling of acceleration and coupling ofbraking comprise an electromagnetic clutch, in which two radial cagescoaxial with the primary shaft, supported respectively by the firsttoothed gear and by the fixed frustoconical bearing surface of thegearbox case, are capable of cooperating selectively in slipping mannerwith two ends of a rotor in two portions integral with the primary shaftto accelerate or brake respectively the primary shaft when a magneticflux is established between a rotor portion and a clutch cage;

the electromagnetic clutch is a metal-powder clutch;

the gearbox is provided with a motorized pump, in which a fixed casesupporting axial pistons is integral with the gearbox case, in which acontrol plate is linked in rotation to the primary shaft of the gearbox,and which is capable of operating selectively as a hydraulic motor orhydraulic pump to accelerate or brake respectively the primary shaft;

the gearbox is a robotized gearbox which is provided with automatedcontrol means acting on the declutchable means for acceleration andbraking of the primary shaft, and automated means for interlocking theidler pinions on the shafts supporting them.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will become clearfrom reading the detailed description hereinafter, which will beunderstood by referring to the attached drawings, wherein:

FIG. 1 is a schematic view in section through a longitudinal centralplane passing through the axes of the two shafts of a gearboxconstructed according to the invention, provided with a noninterlockedidler pinion and a coupling device with contact wheel, illustrated in arest mode;

FIG. 2 is a view similar to FIG. 1, the coupling device beingillustrated in an active mode of acceleration of the primary shaft;

FIG. 3 is a view similar to FIG. 1, the coupling device beingillustrated in an active mode of braking of the primary shaft;

FIG. 4 is a view similar to FIG. 1, the idler pinion being interlockedand the coupling device being illustrated in an inactive mode;

FIG. 5 is a schematic view in section through a longitudinal centralplane of a gearbox constructed according to a variant of the inventionand provided with a device for coupling by friction clutch; and

FIG. 6 is a schematic view in section through a longitudinal centralplane of a gearbox constructed according to another variant of theinvention and provided with a device for coupling by electromagneticclutch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Throughout the description, identical reference numbers denote identicalor similar elements.

In known manner, a gearbox 10 is provided with a case 12 which supportsin rotation two longitudinal parallel shafts, the primary 14 and thesecondary 16. Primary shaft 14 receives motive power from an engine (notillustrated) of the vehicle, while secondary shaft 16 is capable oftransmitting the motive power to at least one wheel 18 of the vehiclevia a transmission 20. An idler pinion 22 supported by primary shaft 14is capable of being interlocked with a fixed pinion 24 of the secondaryshaft to transmit the motive power from primary shaft 14 to secondaryshaft 16. Gearbox case 12 is provided with case end 26, which isprovided with controlled declutchable means 28 for acceleration orbraking of primary shaft 14.

According to a first embodiment, controlled declutchable means 28 areprovided with a toothed gear 40 integral in rotation with one end ofsecondary shaft 16, the said gear engaging with a toothed gear 42, whichis supported in rotation by end 26 of gearbox case 12 and which iscoaxial with primary shaft 14. Toothed gears 40 and 42 are permanentlyengaged, and so toothed gear 42 is indirectly driven in rotation bywheel 18 of the vehicle.

Controlled declutchable means 28 are also provided with a couplingdevice 30, in which a contact wheel 32, provided with a hub 50, islinked in rotation to the primary shaft by splines 34. Contact wheel, 32is capable of being driven slidingly along the primary shaft, and isprovided on two oppositely disposed faces with a first annularfrustoconical bearing surface 36 and a second annular frustoconicalbearing surface 38. An axial sliding gear wheel 48 cooperating with ahub 50 of contact wheel 36 permits its axial sliding movements alongsplines 34 of primary shaft 14 to be controlled.

Coupling device 30 is also provided with a fixed annular frustoconicalbearing surface 44, supported by the end 26 of the gearbox case andcoaxial with primary shaft 14, which passes therethrough. Annularfrustoconical bearing surface 44 is disposed facing first annularfrustoconical bearing surface 36 of contact wheel 32.

Coupling device 30 is also provided, facing second annular frustoconicalbearing surface 38 of contact wheel 32, with an annular frustoconicalbearing surface 46, which is supported by toothed wheel 42 andconsequently is coaxial with primary shaft 14.

In this way, contact wheel 32 of the coupling device is, in anintermediate rest position illustrated in FIG. 1, disposed axiallybetween annular frustoconical bearing surfaces 44 of end 26 of thegearbox case and 46 of toothed gear 42, but is not in contact with thesaid regions.

In fact, gearbox 10 illustrated in FIG. 1 is in a neutral position inwhich idler pinion 22 of primary shaft 14 is not interlocked with fixedpinion 24 of secondary shaft 16. This configuration corresponds to astate in which the vehicle is stopped or is in an intermediate state inwhich another idler pinion (not illustrated) supported by primary shaft14 is interlocked on the primary shaft and in which idler pinion 22, forexample, will subsequently be interlocked on primary shaft 14 to engagea different gear reduction ratio.

In this state, contact wheel 32 occupies an intermediate position alongsplines 34 in which it does not cooperate with any of the elements ofcoupling device 30. Toothed gear 42 is then driven at a speedproportional to that of wheel 18 by the fact of its engagement withtoothed gear 40 of the secondary shaft and of transmission 20.

The view of FIG. 2 illustrates a state in which secondary shaft 16 isturning at substantially greater speed than primary shaft 14. In thisstate the vehicle operator has released the aforesaid idler pinion (notillustrated), declutched and initiated engagement of the gear reductionratio corresponding to idler pinion 22. Primary shaft 14 slows, whilethe secondary shaft is driven by wheel 18 of the vehicle.

In this case, to achieve interlocking of idler pinion 22 on primaryshaft 14 and to cause it to engage with fixed pinion 24 of secondaryshaft 16, by sliding its hub 50 longitudinally along shaft 14, it isnecessary to bring it beforehand to a sufficiently high speed ofrotation that teeth 52 of idler pinion 22 and 54 of fixed pinion 24 cancooperate noiselessly.

For this purpose, controlled sliding gear wheel 48 first moves hub 50 ofcontact wheel 32 toward the left, such that its annular frustoconicalbearing surface 38 cooperates by friction with annular frustoconicalbearing surface 46 of toothed gear 42. In this way, contact wheel 32 isdriven in slipping rotation by toothed gear 42, the speed of which islinked to that of secondary shaft 16. Contact wheel 32 then drivesprimary shaft 14 via splines 34, and brings it progressively to a speedof rotation sufficient to permit interlocking of idler pinion 22 onshaft 14 to engage with fixed pinion 24 of secondary shaft 16, as willultimately be seen with reference to FIG. 4.

The configuration described with reference to FIG. 3 illustrates thecase in which primary shaft 14 is turning at substantially greater speedthan secondary shaft 16.

To achieve interlocking of idler pinion 22 and to permit engagement ofidler pinion 22 with fixed pinion 24, it is necessary to brake primaryshaft 14. This operation is performed by moving sliding gear wheel 48axially toward the right, such that annular frustoconical bearingsurface 36 of contact wheel 32 cooperates by slipping friction withfixed annular frustoconical bearing surface 44 of end 26 of the gearboxcase. In this way, a braking torque is applied to hub 50 of contactwheel 32, and it progressively brakes primary shaft 14, thus permittinginterlocking of pinion 22 and engagement thereof with fixed pinion 24,as described with reference to FIG. 4.

FIG. 4 illustrates the last phase of interlocking of idler pinion 22 onprimary shaft 14 in such a way that it engages with fixed pinion 24 ofsecondary shaft 16.

In this configuration, primary shaft 14 has been brought to an adequatespeed of rotation via coupling device 30. Sliding gear wheel 48 ofcoupling device 30 is then driven in such a way that contact wheel 32once again occupies, as described with reference to FIG. 1, anintermediate rest position between annular frustoconical bearingsurfaces 46 of toothed gear 42 and fixed frustoconical bearing surface44 of end 26 of the gearbox case.

The primary shaft then turns, by virtue of its inertia, at an adequatespeed, and a device (not illustrated) moves idler pinion 22 axiallytoward the left in such a way that it is brought integrally intorotation with primary shaft 14 and that its teeth 52 engage with teeth54 of the fixed pinion of secondary shaft 16, thus permittingtransmission of the motive power originating from the engine (notillustrated) to secondary shaft 16 to drive the vehicle.

This embodiment is particularly advantageous, since it permits simplesynchronization of primary shaft 14 with secondary shaft 16 to beachieved.

Thus, a single device 28, situated at the end of gearbox 12, forexample, or in another place of gearbox 12, permits synchronization ofall of the idler pinions of the gearbox to be achieved. In fact, such adevice is applicable both to idler pinion 22 of primary shaft 14 (as hasbeen described) and to idler pinions that would be supported by thesecondary shaft, since the nature of the operation performed by device28 is synchronization of the speeds of the primary and secondary shaftsto correspond closely to the chosen gear reduction ratio.

Device 28 also permits the compactness and weight of the gearbox to begreatly influenced, since the conventional synchronizer devicesassociated with each idler pinion become superfluous. In fact, a singledevice 28 controls all synchronization operations of the gearbox via anappropriate logical control unit, which adequately directs the movementsof contact wheel 32 via sliding gear wheel 48.

FIG. 5 illustrates an alternative embodiment of the invention. In thisembodiment, the operating principle of controlled declutchable means 28is similar to that described with reference to FIGS. 1 to 4, but thecooperating surfaces are substantially different. Coupling device 30 inthis case comprises a friction clutch, contact wheel 32 comprising aclutch disk covered on its two faces with friction lining, plane annularbearing surfaces 44 of end 26 of the case and 46 of toothed gear 42being plates, made of ground steel, for example.

In fact, contact wheel 32 is provided with two plane annular bearingsurfaces 38 and 36 designed to cooperate with complementary planeannular bearing surfaces 44 and 46. Such a design favorably influencesthe manufacturing costs, since it eliminates the need for constructionof frustoconical surfaces, which are generally costly to machine.

As an alternative (not illustrated), the clutch comprising couplingdevice 30 can advantageously comprise an electromagnetic clutch in whichcontact wheel 32 comprises a rotor and in which toothed gear 42 and end26 of the gearbox case are each provided with a cage coaxial withprimary shaft 14, these cages being able to be traversed by anelectromagnetic flux, which drives the rotor formed by wheel 32. The tworadial cages are supported respectively by the first toothed gear (42)and by the fixed bearing surface (44) of the case (12) of the gearbox(10), and are capable of cooperating selectively in a slipping mannerwith two ends of the wheel (32), which forms a rotor in two portions andwhich is integral with the primary shaft (14) to accelerate or brakerespectively the primary shaft (14) when a magnetic flux is establishedbetween a portion of the wheel (32) forming a rotor and a cage of theclutch.

The electromagnetic clutch under consideration can also be a powder-typeelectromagnetic clutch, the electrical power consumed by such a devicethen being much smaller than that consumed by a conventionalelectromagnetic clutch. Such a device has the advantage that it can becontrolled simply by a logical control unit, which ensuressynchronization of primary shaft 14 with secondary shaft 16.

FIG. 6 illustrates a final embodiment of the invention in whichcontrolled declutchable means 28 are provided with a motorized pump 56,which is disposed at end 26 of the gearbox case and which is linked inrotation to primary shaft 14. In this configuration, declutchable means28 receive power not from secondary shaft 16 but from the engine which,for example, supplies a hydraulic compressor. Motorized pump 56 isprovided, for example, with axial pistons (not illustrated), and it canoperate selectively as a hydraulic motor to accelerate primary shaft 14or as a hydraulic pump to brake primary shaft 14.

This variant is particularly advantageous, since it permitssynchronization of primary shaft 14 with secondary shaft 16 to beachieved by hydraulic means, the power of which is furnished, forexample, by a hydraulic compressor supplied by the vehicle engine. Suchdeclutchable means can therefore be controlled by an extremelysimplified logical control unit involving very few electroniccomponents. These declutchable means are particularly suitable to anautomatic robotized gearbox in which the hydraulic control unitgenerally has a predominant place. Such a robotized gearbox can includeautomatic control means acting on the declutchable means foracceleration and braking of the primary shaft (14), and automated meansfor interlocking of the idler pinions (22).

What is claimed is:
 1. A motor vehicle gearbox comprising: a gearboxcase; a primary shaft having an idler pinion mounted thereon; asecondary shaft provided parallel to said primary shaft, said secondaryshaft being linked to at least one wheel, said secondary shaft having asecond fixed pinion mounted thereon, said idler pinion and said secondfixed pinion being configured to engage one another in order to transferpower from said primary shaft to said secondary shaft; and means forsynchronizing a rotational speed of said idler pinion with a rotationalspeed of said second fixed pinion for facilitating engagement thereof,said means for synchronizing comprising a device selectively permittinga rotational speed of said primary shaft to be increased or decreased inorder to facilitate engagement of said idler pinion with said secondfixed pinion, said device comprising means for temporarily linking saidprimary shaft in slipping rotation to said gearbox case, wherein saiddevice further comprises means for temporarily linking said primaryshaft in slipping rotation to said secondary shaft.
 2. A gearboxaccording to claim 1, characterized in that the means for temporarilylinking the primary shaft in slipping rotation to the secondary shaftare provided with a first toothed gear coaxial with the primary shaft,which engages with a second toothed gear, which is supported by thesecondary shaft and linked in rotation thereto, and which is capable ofbeing temporarily linked in rotation to the primary shaft via a slippingdevice for coupling of acceleration.
 3. A gearbox according to claim 2,characterized in that the means for linking the primary shaft inslipping rotation to the gearbox case are provided with a fixed annularbearing surface of the gearbox case, coaxial with the primary shaft, towhich the primary shaft can be linked temporarily via a slipping devicefor coupling of braking.
 4. A gearbox according to claim 3,characterized in that the slipping device for coupling of accelerationand the slipping device for coupling of braking are provided with acommon contact wheel, which is linked in rotation to primary shaft bysplines, which is provided with two oppositely disposed annular bearingsurfaces, and which is capable of being driven slidingly along theprimary shaft, toward a first active extreme axial position in which afirst annular bearing surface cooperates by friction with acomplementary annular bearing surface of the said first toothed gear, toaccelerate the primary shaft, or toward a second, opposite activeextreme axial position in which a second annular bearing surfacecooperates by friction with the fixed, annular bearing surface of thegearbox case, to brake the primary shaft, by passing through an indexedintermediate axial rest position.
 5. A gearbox according to claim 4,characterized in that the annular bearing surfaces are frustoconical. 6.A gearbox according to claim 4, characterized in that the annularbearing surfaces are plane, and in that the contact wheel is a clutchdisk covered with a friction lining material.